Someone who is close to an obese person is 57 per cent more likely to also become overweight than is someone whose friends and family members are of normal size.
The same pattern seems to repeat itself among siblings, especially if they are of the same sex, while a spouse of an obese person is 37 per cent more likely to gain significant weight than is the husband or wife of a slimmer partner.
Researchers have discovered these 'clusters of obesity' after studying lifestyle surveys that have tracked people's health over the last 30 years.
They are hoping that the opposite might also apply. If obesity spreads through social networks, the same might happen when people start dieting and exercising, too.
(Source: New England Journal of Medicine, 2007; 357: 370-9).